102 ANSWERS TO PRACTICAL QUESTIONS 



(3.) If 321.56 tons (H 2 SO 4 ) is 70 % of the given oil of vit- 

 riol, the entire amount would be 321.56 tons x -^ = 459.28 tons 

 (oil of vitriol). 



247 1. Hoiv would you prove the presence of tannin 

 in tea ? 



By adding a few drops of a solution of ferrous sulphate. 

 This would form a dark precipitate of iron tannate. 



2. How would you test for Fe in a solution ? 



(See MUler's Inorganic Chemistry, p. 625.) 



A solution of nutgalls will give a bluish-black, inky precipi- 

 tate. The ferrous- or proto-salts are distinguished by their light 

 green color, and by their solutions giving (1) a white precipi- 

 tate, with caustic alkalies ; (2) a light blue precipitate, with po- 

 tassium ferrocyanide, which rapidly becomes dark; while the 

 ferric- or per-salts are yellow-colored, and their solutions yield 

 (1) a deep reddish-brown precipitate, with the caustic alkalies ; 

 and (2) a deep-blue precipitate (Prussian blue), with potassium 

 ferrocyanide. 



3. Why can we settle coffee with an egg ? 



The albumen of the egg coagulates by heat, and, entan- 

 gling the particles of coffee, mechanically carries them to the 

 bottom. 



4. How would you show the presence of starch in a 

 potato ? 



A solution of iodine will form the blue iodide of starch. 



5. IVJiy is starch stored in the seed of a plant? 



For the growth of the young plant. 



6*. Why are unbleached cotton goods dark-colored ? 



Because of the dirt gathered in the process of manufacture. 

 The cotton balls are snowy white. 



7. Why do beans, rice, etc. 9 swell when cooked ? 



On account of the bursting of the starch granules. 



8, Wliy does decaying wood darken ? 



